<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>使用 border-radius 画圆形</title>
    <style>
        .demo {
            width: 200px;
            height: 200px;
            border: 1px solid #ccc;
            background-color: #f00;
            margin: 50px auto;
            border-radius: 50%;
        }
    </style>
</head>
<body>
    <div class="demo">

    </div>
</body>
</html>